Methods and apparatus for testing integrated circuits

ABSTRACT

In a first aspect, a first method is provided for testing an integrated circuit (IC). The first method includes the steps of (1) selecting a bit from each of a plurality of memory arrays formed on an IC chip; (2) selecting one of the plurality of memory arrays; and (3) storing the selected bit from the selected memory array. Numerous other aspects are provided.

FIELD OF THE INVENTION

The present invention relates generally to integrated circuit design,and more specifically to methods and apparatus for testing integratedcircuits.

BACKGROUND OF THE INVENTION

An integrated circuit (IC) chip may include one or more memory arraysused to store data. The one or more memory arrays may be grouped in oneor more sets. To test such a chip, an ABIST test may be performed on theIC chip (e.g., to determine whether the IC chip includes any defects).During an ABIST test, a pattern of data is provided to the IC chip andwritten into one or more of the memory arrays (e.g., each memory arrayin a set of memory arrays). The data then is read out of the one or morememory arrays and compared to the data written into the one or morememory arrays. The resulting information is used to determine whether afailure occurred in one or more of the memory arrays.

An IC chip may include additional circuitry for performing an ABISTtest. In one conventional testing configuration, a different latch(e.g., an observation latch) is coupled to each memory array for storingdata that is read from the memory array. In this manner, the pattern ofdata written into a memory array may be read out of the memory array andstored in the observation latch associated with the memory array.

Because each observation latch occupies a large amount of space on an ICchip, including an observation latch for each memory array of the ICchip consumes a sizeable amount of real estate or floor plan area of theIC chip. Accordingly, methods and apparatus for testing integratedcircuits that consume less chip real estate would be desirable

SUMMARY OF THE INVENTION

In a first aspect of the invention, a first method is provided fortesting an integrated circuit (IC). The first method includes the stepsof (1) selecting a bit from each of a plurality of memory arrays formedon an IC chip; (2) selecting one of the plurality of memory arrays; and(3) storing the selected bit from the selected memory array.

In a second aspect of the invention, a second method is provided fortesting an integrated circuit (IC). The second method includes the stepsof (1) selecting a bit from each of a first and second plurality ofmemory arrays formed on an IC chip; (2) selecting one memory array fromeach of the first and second plurality of memory arrays; and (3) storingthe selected bit from the selected memory array for each of the firstand second plurality of memory arrays.

In a third aspect of the invention, a first apparatus is provided thatincludes a plurality of memory arrays, a latch and a selection circuitcoupled to the plurality of memory arrays and to the latch. Theselection circuit is adapted to (1) receive a bit from each of theplurality of memory arrays; (2) select one of the plurality of memoryarrays; and (3) store the bit from the selected memory array.

In a fourth aspect of the invention, a second apparatus is provided thatincludes a first plurality of memory arrays, a first latch and a firstselection circuit coupled to the first plurality of memory arrays and tothe first latch. The first selection circuit is adapted to (a) receive abit from each of the first plurality of memory arrays; (b) select one ofthe first plurality of memory arrays; and (c) store the bit from theselected one of the first plurality of memory arrays.

The second apparatus also includes a second plurality of memory arrays,a second latch and a second selection circuit coupled to the secondplurality of memory arrays and to the second latch. The second selectioncircuit is adapted to (d) receive a bit from each of the secondplurality of memory arrays (e) select one of the second plurality ofmemory arrays; and (f) store the bit from the selected one of the secondplurality of memory arrays. Numerous other aspects are provided inaccordance with these and other aspects of the invention.

Other features and aspects of the present invention will become morefully apparent from the following detailed description, the appendedclaims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a conventional IC chip on which an ABISTtest may be performed.

FIG. 2 is a block diagram of a novel IC chip on which an ABIST test naybe performed in accordance with the present invention.

FIG. 3 is a schematic diagram of exemplary structure of a memory arrayof the IC chip of FIG. 2.

FIG. 4 illustrates an exemplary selection circuit used to select a bitof data from a first plurality of memory arrays of the IC chip of FIG.2.

FIG. 5 illustrates an exemplary operation of the

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a conventional IC chip on which an ABISTtest may be performed. The conventional IC chip 102 may include one ormore memory arrays 110 (Tag-A0), 112 (Tag-A1), 114 (Tag-A2), 116(Tag-A3), 120 (Tag-B0), 122 (Tag-B1), 124 (Tag-B2), 126 (Tag-B3) used tostore data. In one embodiment, the conventional IC chip may includeeight memory arrays. Other numbers of memory arrays may be employed.

During an ABIST test, a pattern of data may be sent to the IC chip 102and written into one or more of the memory arrays 110-126 of the IC chip102. Thereafter, the data is read out of the one or more memory arrays110-126 and compared to the data written to the one or more memoryarrays 110-126. Any discrepancy therebetween may indicate/identify afailure or defective memory array.

The conventional IC chip 102 may include a different latch (e.g., anobservation latch) 130, 132, 134, 136, 140, 142, 144, 146 coupled toeach memory array 110-126, respectively, for storing data read out ofeach memory array during ABIST testing. In the embodiment where theconventional IC chip includes eight memory arrays, the conventional ICchip may include eight latches. As stated, including an observationlatch for each memory array consumes a sizeable amount of real estate ofthe IC chip 102.

FIG. 2 is a block diagram of a novel IC chip 200 on which an ABIST testmay be performed in accordance with the present invention. The IC chip200 may include a first plurality of memory arrays 210 (Tag-A0), 212(Tag-A1), 214 (Tag-A2), 216 (Tag-A3). Other numbers of memory arrays maybe employed.

As will be described further below, during an ABIST test, a pattern ofdata may be sent to the IC chip 200 and written to one or more of thememory arrays 210-216 of the IC chip 200. Each of the one or more memoryarrays 210-216 then may output the data that was written into the memoryarray 210-216. The data output from a memory array may be compared tothe data written to the memory array to identify a failure or defect inthe memory array. The structure of each memory array will be describedbelow with reference to FIG. 3.

The first plurality of memory arrays 210-216 may be coupled to a firstlatch 232 (e.g., an observation latch) via a first multiplexer circuit228. The first multiplexer circuit 228 may selectively output data fromone of the plurality of memory arrays 210-216 to be stored in the firstlatch 232. Therefore, an ABIST test may be performed on that memoryarray of the IC chip 200 by comparing the data stored in the first latch232 (e.g., the data output by the memory array) with the data written tothe memory array.

As stated, the first plurality of memory arrays 210-216 may be coupledto the multiplexer circuit 228. More specifically, the output of each ofthe first plurality of memory arrays 210-216 may be provided to thefirst multiplexer circuit 228 as data inputs. The output of each memoryarray may be one or more bits. Based on signals (e.g., select signals)input to the first multiplexer circuit 228, the first multiplexercircuit 228 may selectively output data input to the first multiplexercircuit 228 by one of the memory arrays 210-216. The first latch 232then stores the data output by the first multiplexer circuit 228. In oneembodiment, each memory array 210-216 outputs thirty-four bits of data.Therefore, the first observation latch 232 may store thirty-four bits ofdata output from one of the memory arrays 210-216. Other memory arrayand/or observation latch sizes may be employed.

Using the novel IC chip 200, the data output from one of a plurality ofmemory arrays may be selected, stored, and observed. The above task isaccomplished by the novel IC chip 200 without requiring a separate latchfor each memory array 210-216. Consequently, the novel IC chip 200 mayrequire fewer latches to perform an ABIST test than the conventional ICchip 100. By reducing the number of latches included in the IC chip onwhich an ABIST test may be performed, less chip real estate is consumed.

In one embodiment, the IC chip 200 may include a second plurality ofmemory arrays 220 (Tag-B0), 222 (Tag-B1), 224 (Tag-B2), 226 (Tag-B3)coupled to a second latch (e.g., an observation latch) 234 via a secondmultiplexer circuit 230. The output of each of the second plurality ofmemory arrays 220-226 may be provided to the second multiplexer circuit230 as data inputs. The second multiplexer circuit 230 then mayselectively output data input from one of the second plurality of memoryarrays 220-226 to be stored in the second latch 234 in a manner similarto that described above with reference to the first plurality of memoryarrays 210-216, the first multiplexer circuit 228, and the first latch232.

In at least one embodiment of the invention, data output from one of thefirst plurality of memory arrays 210-216 may be selected (via the firstmultiplexer circuit 228) and stored in the first latch 232 and dataoutput from one of the second plurality of memory arrays 220-226 may beselected (via the second multiplexer circuit 230) and stored in thesecond latch 234 simultaneously (e.g., in parallel). Therefore, an ABISTtest may be performed simultaneously on more than one memory array. Morespecifically, a memory array from the first plurality of memory arrays210-216 and a memory array from the second plurality of memory arrays220-226 may be included in a set. For example, memory arrays 210 and220, 212 and 222, 214 and 224, and 216 and 226 may be included in afirst, second, third and fourth set, respectively. The ABIST test may beperformed simultaneously (e.g., in parallel) on all memory arraysincluded in a set.

Exemplary structure of the memory array 210 will now be described withreference to FIG. 3. The memory arrays 212-226 may be similarlyconfigured.

With reference to FIG. 3, the memory array 210 includes a plurality ofrows (e.g., word lines 314) that intersect a plurality of columns (e.g.,bit lines 316). In one embodiment, the memory array 210 may includethirty-two word lines and thirty-four bit lines. Other numbers of wordlines 314 and/or bit lines 316 may be included in the memory array 210.The memory array 210 may include an SRAM or similar cell 312 at theintersection (e.g., junction) of each word line 314 and each bit line316 for storing one or more bits of data.

The memory array 210 may include a global dot line 318 coupled to eachbit line 316 for outputting data. More specifically, for each bit line316 the memory array 210 outputs data (stored in a memory cell 312 atthe junction of the bit line 316 and a selected word line 314) via theglobal dot line 318 coupled to the bit line 316. Data may be selected tobe output from the memory array 210 by selecting a word line 314. Forexample, if word line “0” (WL<0>) is selected in the memory array 210,data stored in the memory cell 312 at the junction of word line “0” andeach bit line 316 will be written to and thereafter output from theglobal dot line 318 corresponding to each bit line 316. In the exemplaryembodiment of FIG. 3, the data output from the memory array 210 via theglobal dot line 318 corresponding to bit lines 0-33 of word line 0 is“1”, “0”, “1” . . . “0”, respectively. Consequently, by selecting a wordline in the memory array 210, thirty-four bits of data may be selectedto be output from the memory array 210 (via the global dot lines 318).As stated, each of the memory arrays 210-226 shown in FIG. 2 may operatein a similar manner to output data, and each may output datasimultaneously.

FIG. 4 illustrates an exemplary selection circuit 400 used to select abit of data from the first plurality of memory arrays 210-216 and storethe bit of data in the first observation latch 232. In at least oneembodiment, one such circuit 400 is provided for each global dot linefrom which data may be output from a memory array. For example, if eachmemory array 210-216 includes 34 bit lines, 34 selection circuits 400may be employed to select all 34 bits that may be output by a memoryarray. Consequently, all of the data output from one of the firstplurality of memory arrays 210-216 (via the global dot lines 318) may beselectively output and stored using the selection circuits 400. Theselection circuits 400 may be employed by the second plurality of memoryarrays 220-226 in a manner similar to that employed by the firstplurality of memory arrays 210-216.

With reference to FIG. 4, the selection circuit 400 may be coupled to adecoder 402. The decoder 402 may receive input signals and generate aplurality of selection signals as is known in the art. For example, thedecoder 402 may receive two input signals 11, 12 and output fourselection signals S1, S2, S3, S4.

The selection circuit 400 may include a multiplexer 404 coupled to thedecoder 402; and the selection signals S1, S2, S3, S4 output by thedecoder 402 may be input to the multiplexer 404 and serve as selectsignals for the multiplexer 404. The multiplexer 404 is also coupled toa global dot line 318 of each of the first plurality of memory arrays210-216 via a plurality of inverters 406 a-d, respectively. One globaldot line 318 of each of the first plurality of memory arrays 210-216(collectively referred to as global dots in FIG. 4) is input to themultiplexer 404 as data signals D1, D2, D3, D4. In one embodiment, themultiplexer 404 selects one of the four input signals D1, D2, D3, D4 tooutput based on the select signals S1, S2, S3, S4. Other numbers ofselect signals and/or data signals may be used. The observation latch232 stores the data (e.g., one bit) output by the multiplexer 404.

The multiplexer 404 includes a plurality of stacked transistors N1-N8.The number of stacked transistors is based on the number of memoryarrays from which data is input to the multiplexer 404. In oneembodiment, the multiplexer 404 includes four pairs of stackedtransistors and provides 4-to-1 multiplexing. Other sizes may beemployed. As shown in FIG. 4, a first pair of stacked transistors mayinclude a first n-channel metal-oxide-semiconductor field-effecttransistor (NFET) N1 coupled to a global dot line of memory array 210(via inverter 406 a) and an ABIST dot output line 408. The first pair ofstacked transistors may include a second NFET N2 coupled to the firstNFET N1 and ground. The gate of the second NFET N2 is coupled to theselect signal S1 and is used to select the output of memory array 210for output on the ABIST dot output line 408.

Similarly, a second pair of stacked transistors may include a third NFETN3 coupled to a global dot line of memory array 212 (via inverter 406 b)and the ABIST dot output line 408. The second pair of stackedtransistors may include a fourth NFET N4 coupled to the third NFET N3and ground. The gate of the fourth NFET N4 is coupled to the selectsignal S2 and is used to select the output of memory array 212 foroutput on the ABIST dot output line 408.

A third pair of stacked transistors may include a fifth NFET N5 coupledto a global dot line of memory array 214 (via inverter 406 c) and theABIST dot output line 408. The third pair of stacked transistors mayinclude a sixth NFET N6 coupled to the first NFET N5 and ground. Thegate of the sixth NFET N6 is coupled to the select signal S3 and is usedto select the output of memory array 214 for output on the ABIST dotoutput line 408.

Similarly, a fourth pair of stacked transistors may include a seventhNFET N7 coupled to a global dot line of memory array 26 (via inverter406 d) and the ABIST dot output line 408. The fourth pair of stackedtransistors may include an eighth NFET N8 coupled to the seventh NFET N7and ground. The gate of the eighth NFET N8 is coupled to the selectsignal S4 and is used to select the output of memory array 216 foroutput on the ABIST dot output line 408. Operation of the multiplexer404 is described below.

It should be noted that in one embodiment of the invention each of thedata signals input to the multiplexer 404 may be coupled to pull-upcircuitry (not shown) so that, the initial state value of each of thedata signals D1, D2, D3, and D4 is a logic “1” (e.g., of a high logicstate). Similarly, the ABIST dot output line may be coupled to pull-upcircuitry (not shown) so that, the initial state value of the ABIST dotoutput line 408 is a logic “1” (e.g., of a high logic state).

Using a plurality of the selection circuits 400 shown in FIG. 4, datafrom any one of the first plurality of memory arrays 210-216 may beselectively output and stored in the observation latch 232. For example,each selection circuit 400 may selectively output one bit from onememory array to the observation latch 232, and providing a plurality ofthe selection circuits 400 may allow all bits output by a memory arrayto be selectively output to and stored by the observation latch 232. Thefirst multiplexer 228 thereby may be embodied at least in part as aplurality of selection circuits 400. The second multiplexer 230 may besimilarly embodied with regard to the memory arrays 220-226 and thesecond observation latch 234.

The operation of the novel IC chip 200 is now described with referenceto FIGS. 2-4, and with reference to FIG. 5 which illustrates anexemplary operation of the IC chip 200. With reference to FIG. 5, instep 502 the method 500 begins. In step 504, a bit from each of aplurality of memory arrays is selected. As described with reference toFIG. 3, for a given bit line 316, a bit may be selected from a memoryarray by selecting a word line 314 of the memory array. The memory arraymay output the data stored in the memory cell 312 at the junction of theword line and the given bit line on a global dot line 318 that iscoupled to the given bit line.

In at least one embodiment, the bit selected from each of the firstplurality of memory arrays 210-216 corresponds to the same bit lineand/or word line in each of the memory arrays 210-216. For example, abit stored in a memory cell 312 at the junction of word line “0” and bitline “0” may be selected from each of the first plurality of memoryarrays 210-216.

As shown in FIG. 4, a bit D1, D2, D3, D4 may be selected from each ofmemory array 210-216, respectively. Each of these bits may be input tothe selection circuit 400 of FIG. 4.

In step 506, one of the first plurality of memory arrays 210-216 isselected. More specifically, the signals S1, S2, S3, S4 generated by thedecoder 402 (FIG. 4) are input to the multiplexer 404. As stated, eachsignal S1, S2, S3, S4 may correspond to one of the plurality of memoryarrays 210-216 from which a bit was selected in step 504, and thesignals S1, S2, S3, S4 may serve as select signals. Based on the selectsignals S1, S2, S3, S4, either the data signal D1, D2, D3, or D4 (e.g.,the bit selected from each memory array in step 504) input to themultiplexer 404 is output by the multiplexer 404 on the ABIST dot line408.

In one embodiment, only one of the select signals S1-S4 at a time willbe of a high logic state so that only one bit from one of the memoryarrays (e.g., the “selected” memory array) is output by the multiplexer404. For example, if select signal S1 is of a high logic state (e.g.,“1”) and select signals S2, S3, and S4 are of a low logic state (e.g.,“0”), memory array 210 is selected (e.g., the bit from memory array 210is selected to be output from the multiplexer 404). Because selectsignal S1 has a high logic state, the second NFET N2 turns on. Likewise,because select signals S2, S3, S4 have a low logic state, NFETs N4, N6,and N8 are off.

As mentioned above, in at least one embodiment, the initial state valueof the output of the multiplexer 404 (e.g., the initial value of theABIST dot output line 408) is of a high logic state (e.g., via pull-upcircuitry). Accordingly, if the bit output via the global dot line 318of the first memory array 210 has a high logic state, the gate of thefirst NFET N1 will be low, the first NFET N1 will be off, and the ABISTdot line 408 will remain in its initial state (e.g., high).Alternatively, if the bit output via the global dot line 318 of thefirst memory array 210 has a low logic state, the gate of the first NFETN1 will be high, the first NFET N1 will turn on, and the ABIST dot line218 will be pulled low via the first and second NFETs N1, N2. Bits ofthe other memory arrays may be similarly output to the ABIST dot line408. In this manner, the output signal of the multiplexer 404 will matchthe selected input data signal (e.g., the bit selected from one of thememory arrays in step 504) of the multiplexer 404 for the selected oneof the plurality of memory arrays 210-216.

In step 508, the selected bit from the selected memory array is stored.More specifically, the bit selected to be output from a memory array,which was selected based on a select signal, may be stored in theobservation latch 232 The data output (e.g., the ABIST dot line 408) ofthe multiplexer 404 may be input to the observation latch 232 to bestored. In step 510, the method 500 of FIG. 5 ends.

A bit from one of the second plurality of memory arrays 220-226 may besimilarly selected and stored in the second observation latch 234.Selection of a bit from the first plurality of memory arrays 210-216 andselection of a bit form the second plurality of memory arrays 220-226may be performed simultaneously or in any order. As stated, a pluralityof the selection circuits 400 of FIG. 4 may be employed (e.g., inparallel) to simultaneously read out all bits of a memory array and tostore the bits in an observation latch.

To perform ABIST testing a data pattern may be written into one or moreof the memory arrays 210-216 and/or 220-226 and selectively read out andstored in the observation latch 232 and/or 234 (e.g., using the method500 of FIG. 5). The contents of the respective observation latch thenmay be compared to the original data pattern to test proper operation ofthe selected memory array.

Through the use of the novel IC chip 200 and method 500 of FIG. 5, ABISTtesting may be performed on one or more memory arrays with a reducednumber of latches. For example, if the IC chip 200 performs multiplexingon the global dot lines from each of four memory arrays, the number oflatches needed in the IC chip may be reduced by a factor of 4. Asmentioned above, reducing the number of latches included in the IC chip200 reduces the floor plan area used by ABIST test circuitry and allowschip real estate to be used more efficiently.

The foregoing description discloses only exemplary embodiments of theinvention. Modifications of the above-disclosed apparatus and methodswhich fall within the scope of the invention will be readily apparent tothose of ordinary skill in the art. For instance, the method 500 of FIG.5 may be performed simultaneously on more than one plurality of memoryarrays. In one embodiment, a memory array from a first plurality ofmemory arrays and a memory array from a second plurality of memoryarrays may be grouped in a set. In this manner, an ABIST test may beperformed simultaneously on memory arrays included in the same set(e.g., memory array 210 and memory array 220 of FIG. 2).

Further, although FIG. 2 only discloses two memory arrays (e.g., memoryarray 210 and memory array 220) in a set, a set may include more thantwo memory arrays. Additionally, although the present methods andapparatus disclose performing 4-to-1 multiplexing on the global dotlines of four memory arrays, global dot lines from a larger or smallernumber of memory arrays may be multiplexed.

Accordingly, while the present invention has been disclosed inconnection with exemplary embodiments thereof, it should be understoodthat other embodiments may fall within the spirit and scope of theinvention as defined by the following claims.

1. A method for testing an integrated circuit (IC) comprising: selectinga bit from each of a plurality of memory arrays formed on an IC chip;selecting one of the plurality of memory arrays; and storing theselected bit from the selected memory array.
 2. The method of claim 1wherein selecting a bit from each of a plurality of memory arraysincludes selecting a wordline in each of the plurality of memory arrays.3. The method of claim 1 wherein selecting a bit from each of aplurality of memory arrays includes overwriting an initial state bitvalue of a selection circuit with a value of the selected bit.
 4. Themethod of claim 1 wherein storing the selected bit from the selectedmemory array includes storing the selected bit from the selected memoryarray in a latch.
 5. The method of claim 4 wherein storing the selectedbit from the selected memory array includes one of storing an initialstate bit value of an output of a selection circuit and storing amodified initial state bit value of the output of the selection circuitin the latch.
 6. The method of claim 1 wherein selecting a bit from eachof a plurality of memory arrays formed on an integrated circuit chip,selecting one of the plurality of memory arrays, and storing theselected bit from the selected memory array are performed during anABIST test of the integrated circuit chip.
 7. A method for testing anintegrated circuit (IC) comprising: selecting a bit from each of a firstand second plurality of memory arrays formed on an IC chip; selectingone memory array from each of the first and second plurality of memoryarrays; and storing the selected bit from the selected memory array foreach of the first and second plurality of memory arrays.
 8. The methodof claim 7 wherein selecting a bit from each of the first and secondplurality of memory arrays includes selecting a wordline in each of thefirst and second plurality of memory arrays.
 9. The method of claim 7wherein selecting a bit from each of the first and second plurality ofmemory arrays includes: overwriting a first initial state bit value witha value of the selected bit from the selected memory array of the firstplurality of memory arrays; and overwriting a second initial state bitvalue with a value of the selected bit from the selected memory array ofthe second plurality of memory arrays.
 10. The method of claim 7 whereinstoring the selected bit from the selected memory array for each of thefirst and second plurality of memory arrays includes: storing theselected bit from the selected memory array of the first plurality ofmemory arrays in a first latch; and storing the selected bit from theselected memory array of the second plurality of memory arrays in asecond latch.
 11. The method of claim 10 wherein storing the selectedbit from the selected memory array of the first plurality of memoryarrays includes one of storing an initial state bit value of an outputof a first selection circuit and storing a modified initial state valueof the output of the first selection circuit in a first latch; andwherein storing the selected bit from the selected memory array of thesecond plurality of memory arrays includes one of storing an initialstate bit value of an output of a second selection circuit and storing amodified initial state value of the output of the second selectioncircuit in a second latch.
 12. The method of claim 7 wherein selecting abit from each of a first and second plurality of memory arrays formed onan IC chip, selecting one memory array from each of the first and secondplurality of memory arrays, and storing the selected bit from theselected memory array for each of the first and second plurality ofmemory arrays are performed during an ABIST test of the IC chip.
 13. Anapparatus comprising: a plurality of memory arrays; a latch; a selectioncircuit coupled to the plurality of memory arrays and to the latch, andadapted to: receive a bit from each of the plurality of memory arrays;select one of the plurality of memory arrays; and store the bit from theselected memory array.
 14. The apparatus of claim 13 further comprisinga decoder coupled to the selection circuit.
 15. The apparatus of claim14 wherein the decoder is adapted to generate signals used to select oneof the plurality of memory arrays.
 16. The apparatus of claim 13 whereinthe selection circuit comprises a multiplexer.
 17. An apparatuscomprising: a first plurality of memory arrays; a first latch; a firstselection circuit coupled to the first plurality of memory arrays and tothe first latch, and adapted to: (a) receive a bit from each of thefirst plurality of memory arrays; (b) select one of the first pluralityof memory arrays; and (c) store the bit from the selected one of thefirst plurality of memory arrays; a second plurality of memory arrays; asecond latch; a second selection circuit coupled to the second pluralityof memory arrays and to the second latch, and adapted to: (d) receive abit from each of the second plurality of memory arrays; (e) select oneof the second plurality of memory arrays; and (f) store the bit from theselected one of the second plurality of memory arrays.
 18. The apparatusof claim 17 further comprising a decoder coupled to the first and secondselection circuits.
 19. The apparatus of claim 18 wherein the decoder isadapted to generate signals used to select one memory array from each ofthe first and second plurality of memory arrays.
 20. The apparatus ofclaim 17 wherein the first and second selection circuit comprisemultiplexers.
 21. The apparatus of claim 17 wherein the first and secondselection circuits are adapted to perform (a)-(c) and (d)-(f)simultaneously.